Suspended core subwavelength fibers: towards practical designs for low-loss terahertz guidance

Abstract

In this work we report two designs of subwavelength fibers packaged for practical terahertz wave guiding. We describe fabrication, modeling and characterization of microstructured polymer fibers featuring a subwavelength-size core suspended in the middle of a large porous outer cladding. This design allows convenient handling of the subwavelength fibers without distorting their modal profile. Additionally, the air-tight porous cladding serves as a natural enclosure for the fiber core, thus avoiding the need for a bulky external enclosure for humidity-purged atmosphere. Fibers of 5 mm and 3 mm in outer diameters with a 150 µm suspended solid core and a 900 µm suspended porous core respectively, were obtained by utilizing a combination of drilling and stacking techniques. Characterization of the fiber optical properties and the subwavelength imaging of the guided modes were performed using a terahertz near-field microscopy setup. Near-field imaging of the modal profiles at the fiber output confirmed the effectively single-mode behavior of such waveguides. The suspended core fibers exhibit transmission from 0.10 THz to 0.27 THz (larger core), and from 0.25 THz to 0.51 THz (smaller core). Due to the large fraction of power that is guided in the holey cladding, fiber propagation losses as low as 0.02 cm(-1) are demonstrated specifically for the small core fiber. Low-loss guidance combined with the core isolated from environmental perturbations make these all-dielectric fibers suitable for practical terahertz imaging and sensing applications.

A High Birefringent Polymer Terahertz Waveguide: Suspended Elliptical Core Fiber

“…Moreover, the proposal for the THz fibers based on a suspended elliptical core structure indicates a method to achieve unique property for THz fibers with complex cross section. Finally, we note that the fabrication of such THz fiber designs could be realized by several methods, such as a capillary stacking technique, a polymer casting technique, a hole drilling technique, a combination of drilling and stacking, and so on [11,19].…”

“…Recently, some suspended core THz fibers are reported, which aim to provide low-loss THz guidance [11,12]. Considering the potential applications of a high birefringent THz waveguide, a suspended elliptical core THz fiber which incorporates an elliptical core suspended inside a large porous outer cladding is proposed in the paper.…”

Hybrid metal wire–dielectric terahertz waveguides: challenges and opportunities [Invited]

“…Different types of THz waveguides and fibers have been proposed based on this concept. The simplest of such waveguides is a subwavelength fiber [2][3][4] that features a dielectric core that is much smaller than the wavelength of guided light. As a result, a high fraction of modal power is guided outside of the lossy material and in the low-loss gaseous cladding.…”

Active Terahertz Two-wire Waveguides

“…To date, several THz waveguides have been reported based on dielectric and metallic structures. On the one hand, dielectric based waveguides such as sapphire fibers [1], plastic ribbon waveguides [2] and sub-wavelength fibers [3,4] are not suitable for low dispersion propagation of THz pulses due to the inherent dispersive properties and losses at frequencies above 1 THz. Although hollow core dielectric fibers can boost low-loss and low-dispersion, they are limited in bandwidth due to resonances or bandgap effects [5].…”